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Continuous banging noise in house plumbing when sprinkler is running

Hi
I have installed my system, everything looks good expect one thing, the continuous banging noise in house plumbing when the system is running.

I am in Toronto, water meter is in basement,I connected a 3/4" pipe after the meter to garage, where it supplies the sprinkler system. I have a washroom right above the meter, when the system is running, I can here big banging noise in the washroom, but can barely hear it in garage. Also, the noise is a lot weaker in the basement around the water meter. The frequency of the noise changes when zone changes, the frequency is about 4-5 bangs per second.

Banging is usually an oscillation. Valve opens, water rushes through, and the pressure upstream of the valve drops to a point where the valve no longer stays fully opened, and a nearly-closed zone valve brings the supply pressure back up again. This repeats and you get the banging.

Make certain that every shutoff valve in the pathway to your sprinklers is fully opened.

Are your zone valves flow-control types? Throttling down the flow controls will make a difference here.

Banging is usually an oscillation. Valve opens, water rushes through, and the pressure upstream of the valve drops to a point where the valve no longer stays fully opened, and a nearly-closed zone valve brings the supply pressure back up again. This repeats and you get the banging.

Make certain that every shutoff valve in the pathway to your sprinklers is fully opened.

Are your zone valves flow-control types? Throttling down the flow controls will make a difference here.

Very simply put, sprinkler systems should not be operating with banging plumbing. If you are betting the ranch that there are no partially-closed valves in the supply chain, and you have no flow-controls on the zone valves (very bad choice on the part of the installer, by the way) then all there is left to play around with is the flow in the zones that are doing the banging. You are trying to find a point of lower flow rates where the banging ceases.

Thanks wet_boots. I am just surprised how that was possible. I have 3/4" pipe with static 65 PSI, The maximum GPM r zone in the design is only 6.12 GPM. In theory, a 1/2" pipe should be able to handle the GPM.

Very simply put, sprinkler systems should not be operating with banging plumbing. If you are betting the ranch that there are no partially-closed valves in the supply chain, and you have no flow-controls on the zone valves (very bad choice on the part of the installer, by the way) then all there is left to play around with is the flow in the zones that are doing the banging. You are trying to find a point of lower flow rates where the banging ceases.

My only input is to think about is. Do you have a Pressure Reducing Valve? If you do it's possible it has failed and preventing the full amount of flow available being allowed into the sprinkler system . It's also possible if there is a PRV on the cities side and it has failed ( I've dealt with 3 failed PRV's this past week and half so they are fresh in my mind)

Can you cut your main line on the irrigation side and get a flow rate test?

Does every zone cause the banging? I'm highly leaning towards flow restriction either from a PRV or a shut off not fully open.. Make sure your water meter is fully on too

I also recommend to get a dynamic pressure reading when the sprinkler zones are running

dynamic PSI after the double check valve and before the master valve: 35-44 PSI (different zone has different readings)

Flow test:
filled a 5 gallon bucket in 25 seconds, so the GPM should be at least 10 GPM, higher than any of the zones, and this 10 GPM comes from a 1/2" outlet, the sprinkler zone has all the way 3/4" pipe.

The maximum flow rate is zone 7, it use less than 7 gallon water per minute. The GPM of the supply pipe is at least 10, so in theory, I should have enough water to feed the system, am I correct?

Where the noise come from? from the zone valve? Master valve? double check valve? or water meter?

All zone valves including master valve are 1", I use a 1" to 3/4" fitting to connect it to the 3/4" pipe.

I have also noticed when the system switches zones (e.g. zone 1 is closing and zone 2 is starting), the banging noise goes faster (e.g 8 beats per second) and after 2 seconds (I guess zone 1 is fully closed), the banging noise slows down to a fixed frequency (e.g 4 beats per second).

The banging frequency is different on different zones, some are 4-5 beats per second, some are faster.

I have also noticed that static PSI drops 5 (from 65 to 60) after double check valve. is it normal? I just installed the double check valve myself, did not do any test or anything, should I get some plumber to get it tested?

I also talked to my neighbor, he has the same banging noise for years, I listened to it, it's the same kind of banging noise.

My only input is to think about is. Do you have a Pressure Reducing Valve? If you do it's possible it has failed and preventing the full amount of flow available being allowed into the sprinkler system . It's also possible if there is a PRV on the cities side and it has failed ( I've dealt with 3 failed PRV's this past week and half so they are fresh in my mind)

Can you cut your main line on the irrigation side and get a flow rate test?

Does every zone cause the banging? I'm highly leaning towards flow restriction either from a PRV or a shut off not fully open.. Make sure your water meter is fully on too

I also recommend to get a dynamic pressure reading when the sprinkler zones are running

This post has been edited 1 times, last edit by "brisk" (Jul 13th 2011, 7:16am)

I had a kind of similar situation; Kind of because only 2 of 6 zones made the clanging. First, I tried to look at the backflow, but it checked out fine. Then I reduced the flow, but thought the same thing it should be able to handle it. I ended up going to the master valves and changing the diaphragm, it helped a little. Then I went to the two problem zones and changed the diaphragms and the problem was fixed. It is odd to have that many that need to be changed at once, but odd things happen.

Can't explain the neighbor situation either unless you both have old or inferior valves. Maybe your water is really tough on irrigation materials.
Good Luck